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I'm asking this here to avoid being conned by "professional" roofers in India who either exaggerate their estimates or send highly unskilled labourers to do the job.

This is the layout of a roof:
enter image description here

D: Areas that are damaged
H: Drainage holes
P: Ponding areas (places where water accumulates and does not flow away)
C: Small cracks that may or may not be significant for consideration

D2 was an area where a solar water heater was installed and after it was removed, one strip of the roofing got damaged and cement was applied on it (as in the pic below). It hasn't caused any leak problems for 5 years, and the area only started leaking during last year's rains.
enter image description here

H1 and H2 are the only points for water drainage on the entire roof (I do believe the roof is slightly sloping toward H1 and H2). Because of D2 having some elevation, some of the water collecting in P1 was not able to flow to H2 (blue arrow) and was not flowing to H1 either. enter image description here enter image description here

Water also collects in area P2 and there's no scope for drainage. enter image description here Other areas of damage are at D1 and D3
enter image description here
enter image description here

This is the dampness caused on the ceiling right below D2. There is no leakage anywhere else inside the house:
enter image description here

There are also some slight cracks on the plaster on the ceiling:
enter image description here

Queries:
1. Is it possible that the damages at D1 and D3 could cause water to seep into the damaged areas and eventually flow and accumulate at the D2 area, thus causing leakage inside the house?
2. A mason says that in order to waterproof D2, he'd first have to chip off some of the cement along that strip, then get some sand and cement and mix some waterproofing liquid (another mason said he'd mix a waterproofing powder) into the cement and then apply it over D2. He's offering to do it (and the repairs of D1 and D3) at less than half the price that professional roofers charge. Does his technique sound ok to you?
3. Is it ok if there is some ponding of water at P1 and P2 or should some cement be applied at least at P1, just to create a slope so that the water flows into H2 (won't that add extra weight to the roof)?
4. How does one determine whether cracks are just cracks on the plaster or whether they are deep enough to cause roof leaks? For example, the pictures below:
enter image description here enter image description here

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  • I would want to clean the crack areas and damaged areas and fill both with hydraulic cement. I would then clean the ponding areas and level with self leveling cement. After that I would have the surface coated with hot tar or a painted membrane type of sealer
    – Ed Beal
    Mar 5, 2016 at 11:53
  • Thanks. "hydraulic" cement is the same as "portland" cement, right? Can it directly be mixed with water and used or does it require sand too? The mason had initially said he'd need sand and cement powder and waterproofing liquid which he'd mix into the cement powder. Something like this: youtube.com/watch?v=JWv6FzId9oM From videos I assume that the self levelling cement also does not require sand. But the masons are just ordinary uneducated labourers like in the video, who don't know much of tech stuff.
    – Nav
    Mar 5, 2016 at 15:32

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I mostly agree with Ed Beal. Small or hairline Cracks like C1 & C2 can be simply Caulked for a 10-plus year repair & yes you want to address all of those types of cracks whether they're on the wall or roof, so they don't become bigger cracks. You've got hundreds & ALL cracks are potential leaks.

Break-outs & fully open large splits & spalls like D1 & D3 need to be cleaned of all loose debris & forcibly filled with Hydraulic Cement, it slightly expands within & behind as it cures to make the best water-tightness & backing of the surrounding cement.

Areas like P1 that are in the field of the roof need to be leveled to each side of the low spot's high spots, pitched. Meaning, the P1 outside edge further from H1 will & must be slightly higher than P1's inner closer edge to H2. The entire roof should be shaped like 2 bath tub bottoms with H1 & H2 being the drains.

P2 is quite a bit different since it's blocked by a wall. P2 must be pitched into the roof field with the area at the back of the wall being significantly higher than the area at the front end of the wall. At the front end of the wall P2 then needs to be pitched inward or toward H2.

Your roof must tilt from the front to the back & must also be bellied down from the center & outside walls while always maintaining that front to back pitch in order for H1 & H2 to remove all water & have no puddling. Then, everything can be re-painted & the roof can be sealed.

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  • Thanks lggy, but would D1 & D3 really need hydraulic/portland cement? Because according to this video youtube.com/watch?v=8BSkWrowWW8 and this video youtube.com/watch?v=cxvXsiszTjM, it's mortar that should be used when working with bricks.
    – Nav
    Mar 5, 2016 at 16:57
  • Nope, you don't "need" to use Hydraulic Cement, it's just the best option. You can use Portland Cement or Type S or Type N or Stucco mix. As long as you fill it in & seal it up, you're okay to go, but not best to go.
    – Iggy
    Mar 5, 2016 at 19:51
  • Thanks. I've been searching for hydraulic cement, but it doesn't seem available here. So portland it is. Choosing a 1:2 cement:sand ratio and using a 1:20 waterproofing-liquid:water ratio. I understand the sand acts as a filler and the silica in it reacts with the cement to give more tensile strength. The waterproofing liquid is just to increase the plasticity. Would also need to level area P1 so that water flows to H1.
    – Nav
    Mar 7, 2016 at 4:59
  • That should all work out just fine. Wet or moisten the area down just before placing cement. Make sure you shove & push cement actually into everything you can for D1 & D3, just "covering" them won't have any grip or holding power. 2-coats for D3 might be best, so cement doesn't just fall out from it's own weight. And, use a wet sponge on the patches to smooth them out, but more importantly to feather & seal the edges flat & tight to surrounding areas...especially P1.
    – Iggy
    Mar 7, 2016 at 10:34

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